Roads were expected to be slickest in the lowest elevations of Salt Lake and Utah counties with freezing rain also expected in the Heber Valley. Hazardous roads also were likely on Interstate 80 between Salt Lake City and Grantsville and on Interstate 15 from Salt Lake City to Farmington.
"Plan on leaving early [Thursday] and expect slick and icy conditions," Merrill said.
North of Farmington, the storm was expected to bring snow rather than ice, but freezing rain is possible.
The early freezing rain is expected to switch mid-morning to snow, which likely will accumulate for the evening commute, Merrill said. Snow totals in the valleys were expected to reach 2 to 5 inches.
The reward will be clean air. Air quality in northern Utah counties has been rated unhealthy, or unhealthy for sensitive groups, since last Thursday, according to the Utah Division of Air Quality.
Christine Kruse, a meteorologist with the National Weather Service, said that a storm arriving Wednesday night will clear the air, leaving it a relatively uniform temperature and pressure at all lower altitudes during the storm. That means pollution won't remain trapped on the valley floors. Kruse said the air could begin to improve by Wednesday night and by Thursday should be significantly better.
Air quality ultimately will reach a comparatively pleasant "moderate" quality, according to the Division of Air Quality.
The storm was expected to bring 8 to 12 inches of snow to the Wasatch and Uinta mountains.
Temperatures were expected to reach the low to mid-thirties Thursday throughout the storm area.
The storm will blow through by Friday, with cloudy skies and temperatures in the 30s persisting.
The Utah Avalanche Center reported a moderate risk of snow slides Wednesday along the Wasatch Front, as well as in Cache County and the Uintas.